#define  _CRT_SECURE_NO_WARNINGS

#include<stdio.h>

int main()
{
    int i = 0;
    for (i = 0; i < 4; i++)
    {
        int sum = 0, arr[4] = { 0 };
        arr[i] = 1;
        if ((arr[1] == 0 && arr[3] == 1) || (arr[1] == 1 && arr[3] == 0))
            sum++;
        if ((arr[1] == 0 && arr[2] == 1) || (arr[1] == 1 && arr[2] == 0))
            sum++;
        if ((arr[0] == 0 && arr[1] == 1) || (arr[0] == 1 && arr[1] == 0))
            sum++;
        if (arr[3] == 1 || arr[3] == 0)
            sum++;
        if (sum == 4)
        {
            if (i == 0)
                printf("A\n");
            else if (i == 1)
                printf("B\n");
            else if (i == 2)
                printf("C\n");
            else if (i == 3)
                printf("D\n");
        }
    }

    return 0;
}